Collaborative study was undertaken at Bicetre and at Northwestern University Medical Center (Chicago) to identify the nature and cellular distribution of sterid receptors in isolated epithelium and stroma human prostate. In Bicetre, technics for specific "enzyme markers" have been developed and their reliability has been verified on purified epithelial and stromal preparations. Optimal methods for the quantitation of steroid receptors, intended to avoid inactivation of receptor sites produced by incubation of cell subfractions under "exchange" conditions, have been developed. They will be applied to normal human prostate and BPH samples both at Bicetre and Chicago, and correlated with tissue morphology and marker enzyme assays.